The present invention relates to improvements for a plug used to form a seal for tubes, pipes and similar conduits which transport steam, liquid or gases under pressure.
An earlier version of this type of plug commercially exploited by the present Applicant is disclosed in previous U.S. Pat. Nos. 4,653,540 and 5,289,851, the specifications of which are hereby incorporated by reference. The plug disclosed in U.S. Pat. No. 4,653,540 comprises a hollow housing member which has at one end a relatively large open bore surrounded by a thin wall, and a relatively smaller threaded bore which communicates with the larger bore. An insert member is provided which, in use, is threaded into the smaller bore thereby causing a tapered member, which may be formed on the insert member, to engage the open end of the large bore causing it to expand and bear against the wall of a heat exchanger tube into which the heat exchanger tube plug has been inserted. During use, the housing member is prevented from rotating relative to the heat exchanger tube by means of an eccentric assembly which is mounted on the end of the housing member. At the other end, the insert member has a cylindrical portion and a centrally disposed, integrally formed nut portion. The nut is proportioned to be grasped by a wrench for screwing the insert member into the housing member. The disclosure also suggests that instead of the projecting nut portion, a hexagonal recess may be formed in the end of the cylindrical portion for insertion of a hex wrench or similar tool. The insert member is specified as being integrally formed. A coil spring 34 surrounds the eccentric ring 36 to provide locking engagement against the inner surface of the heat exchanger tube.
The clutch spring on the eccentric ring was abandoned in the production model of this plug. Instead, a knurled outer surface for the eccentric  ring and also short axial grooves on the plug body were added in order to prevent slipping when the eccentric cam actuated.
Also, annular grooves were added to the plug body to increase the sealing potential of the plug. If the plug was installed in a tube that had corrosion, then the raised portion of the serration would cut through any scale and would be stored in the groove thereby enhancing the mechanical contact seal.
Early on during manufacture of the plug defined in U.S. Pat. No. 4,653,540, the plugs had a machined male hex that would accommodate a {fraction (11/32)} inch socket. This, however, proved unsatisfactory because the sockets split and could not be turned down to a diameter in order to fit in any tube smaller than ½ inch. This would be necessary when the plug is recessed within the end of a tube to be sealed. The next design evolution entailed broaching a ¼ inch female square drive in plugs from 460 inches to 0.610 inches in diameter and a ⅜ inch square drive in all plugs 0.620 inches and larger.
U.S. Pat. No. 5,289,851 describes a tube plug that can be provided in dimensions down to 0.420 inches, yet which permits installation torque values of up to 700 inch pounds. In this improved plug, the insert member as disclosed in U.S. Pat. No. 4,653,540, has been replaced with a T45 Torx® socket head screw combined with a separately machined cone having an internal passage threaded to match the threads of the screw. A T45 Torx® drive can be torqued to 764 inch pounds before failure which permits a recommended installation value of up to 700 inch pounds to be utilized.
In both U.S. Pat. Nos. 4,653,540 and 5,289,851 a tool is required to engage the insert member, and specifically, the recess portion or nut of the insert member, in order to screw the insert member into the housing member. Typically, the insert member includes a recess, such as a T45 Torx® socket head recess or a hexagon socket head recess, to engage the tool. However, such an arrangement creates a fair amount of slippage which can complicate the process of screwing the insert member into the housing member, especially in light of the high torsional forces that are being used. Thus, in order to reduce slippage between the tool and the recess of the insert member, an adhesive, such as a drive holding  compound, may be applied to the recess or the end of the tool that engages the recess. However, applying such an adhesive is cumbersome and messy.
It would therefore be an improvement in this art if a tube plug having an insert member were provided with a tool for securely engaging the insert member without the need for an adhesive.